The present invention relates to an optical pick-up for writing/reading data to/from an optical disk.
Well known techniques for detecting signals from optical disks have advantages and also disadvantages.
Such advantages and also disadvantages surface, particularly, for optical disk drives to drive several types of optical disks.
In detail, a differential push-pull (DPP)-tracking error detection technique is used for DVD-R (rewritable DVD) when no data have been recorded.
The DPP-tracking error detection technique, however, produces only a small amplitude in tacking error signals, thus resulting in inadequate servo characteristics, for signal reproduction from ROM disks, such as, DVD-Videos. Because ROM disks have pits the depth of which is decided for a phase-difference detection (DPD)-tracking error detection technique.
For signal detection from DVD-R and ROM disks, optical disk drives, therefore, require both DPP and DPD-tracking error detection mechanisms.
An astigmatism-focus detection technique with the DPP- and DPD-tracking error detection can be achieved by a relatively simple configuration of optical system.
However, this technique raises problems, for land and groove recording-type optical disks, such as, DVD-RAM disks recorded with data in both lands and grooves, such that signals from an optical pick-up when traversing tracks on the optical disks in seeking would be mixed with focus error signals.
Providing detection mechanisms for every type of optical disks on one optical disk drive, for solving such problems results in a complex optical system, a number of signal lines from a photodetector, several stages of I/V amplifiers for current-to-voltage conversion of signals from the optical detector and arithmetic circuitry, and so on.
Moreover, such an optical disk drive has other problems when installing another detection mechanism for rewritable optical disks.
In detail, rewritable optical disks are recorded with wamble signals with undulation in the direction of tracks by groove-modulation and also address signals in pits for address management. These signals are, however, easily distorted by positional displacements in optical axis and optical detector, etc.
A purpose of the present invention is to provide an optical pick-up for detecting signals from several types of optical disks by using detection techniques, such as DPD, DPP and SSD (spot-size detection).
The present invention provides an optical pick-up including: a condenser lens to accept three laser beams reflected on an optical disk; a holographic device to accept the three laser beams via the condenser lens, a surface of the holographic device being divided into a first and a second hologram region by a bisecting line oriented almost parallel to track formed on the optical disk, thus generating xc2x11th-order diffracted light beams on the hologram regions; and a photodetector to accept the xc2x11th-order diffracted light beams to detect signals recorded on the optical disk, the photodetector having a plurality of photo-detecting segments corresponding to the xc2x11th-order diffracted light beams.